Inkjet printers form an image, either monochromatic or in color, by discharging small droplets of ink from one or more inkjet printheads onto desired positions of a printing medium. Generally speaking, inkjet printers may be classified into two types, namely, a shuttle type inkjet printer and a line printing type inkjet printer. A shuttle type inkjet printer includes an inkjet printhead that reciprocates back and forth along a direction perpendicular to the moving direction of a printing medium in order to print an image on the printing medium. The line printing type inkjet printer, which has been developed with relatively higher printing speed in mind, on the other hand, includes a printhead or printheads that remains generally stationary, the collective length of which spans substantially the width of a printing medium so as to allow the stationary printhead(s) to print one or more lines of image across the width of the printing medium as the printing medium advances past the printhead unit.
A particular type of printhead, typically referred to as an “array type printhead,” that includes a number of printheads arranged into an array may be used more often in a line printing type inkjet printer where the collective length of the array substantially covers the width of a piece of printing paper, for example, to further improve upon the printing speed and/or resolution. An array type printhead may also be employed in some shuttle type inkjet printers to improve the printing speed and/or the resolution, in which case, the array type printhead may have a collective length that is smaller than the width of the printing medium.
Inkjet printheads themselves may broadly be classified into one of two types according to the mechanism for the discharging of the ink droplets. The first of which two generally types is often referred to as a “thermal inkjet printhead,” which generates bubbles in the ink with application of heat source, and which discharges the ink droplets by an expansive force of the resulting bubbles. The second type is referred to as a “piezoelectric inkjet printhead,” which includes a piezoelectric material, and which discharges the ink droplets by a pressure applied to ink due to the deformation of the piezoelectric material.
The general discharging mechanism of ink droplets in the thermal inkjet printhead in relevant aspects may be as follows. When a pulse type current is allowed to flow through a heater typically formed of a resistive heating element, the resulting heat generated in the heater causes the ink adjacent to the heater to be rapidly heated to a high temperature, for example, to about 300° C. As a result, the ink starts to boil, generating ink bubbles, which as they expand applies pressure to the ink confined in an ink chamber. The pressure causes the ink in the vicinity of a nozzle to be discharged from the ink chamber in the form of droplets ejected through the nozzle.
By way of an example, referring to the schematic cross-sectional views of FIGS. 1 through 6B, a conventional method of manufacturing a known thermal inkjet printhead will be briefly described. In these drawings and as well as in the associated descriptions below, for the sake of brevity, only one ink chamber structure is depicted and described. However, it should be understood and well known to those skilled in the art that an inkjet printhead may include a large number of ink chambers and the associated nozzles.
Referring to FIG. 1, a chamber layer 12 may be formed on a substrate 10. The chamber layer 12 defines the ink chamber in which the ink to be discharge is filled, and may be formed by coating a chamber layer material on the substrate 10 to a predetermined thickness and by patterning the coated chamber layer material. Referring to FIG. 2, a sacrificial layer 15 may subsequently be formed on the substrate 10 and the chamber layer 12 so as to fill the ink chamber formed in the chamber layer 12. The sacrificial layer 15 may be formed by coating a sacrificial layer material on the substrate 10 and the chamber layer 12 to a predetermined thickness. Referring to FIG. 3, the sacrificial layer 15 and/or the chamber layer 12 may be planarized using, e.g., chemical mechanical polishing (CMP). Referring to FIG. 4, a nozzle layer 16 that includes a nozzle 17 may be formed on the planarized chamber layer 12 and sacrificial layer 15. More specifically, the chamber layer 12 and the sacrificial layer 15 a may be coated with a nozzle layer material of a predetermined thickness, which is then patterned using photolithography so as to form the nozzle 17, to thereby complete the formation of the nozzle layer 16. Then, the sacrificial layer 15 is removed using a solvent to form the ink chamber 13 in the chamber layer 12 as illustrated in FIG. 5. Referring to FIGS. 6A and 6B, the substrate 10 may then be etched to form an ink feedhole 11 through which ink is supplied to the ink chamber 13. With the formation of the feed hole 11, the process of the manufacture of the inkjet printhead may substantially be complete. FIGS. 6A and 6B are cross-sectional views of the completed inkjet printhead cut in directions perpendicular to each other.
In the above described conventional method of manufacturing, and in the resulting conventional thermal inkjet printhead, the thickness of the chamber layer 12 may be determined only by the CMP process. However, it can be difficult to obtain a uniform thickness of the chamber layer 12 by a typical CMP process, and attempts to improve upon the uniformity may come at an added manufacturing costs. moreover, the coating and the removal of the sacrificial layer 15 may add unnecessary complication to the manufacturing process, and may adversely impact the yield.
Another conventional method of manufacturing of a thermal inkjet printhead and the resulting conventional thermal inkjet printhead are illustrated in reference to FIGS. 7 through 9B. Again, for brevity, only one ink chamber and only one nozzle are depicted and described.
Referring to FIG. 7, a chamber layer 22 may be formed on a substrate 20. The chamber layer 22 defines an ink chamber in which ink to be discharged is filled. An ink feed hole for supplying ink to the ink chamber is formed in the substrate 20 as described earlier. The chamber layer 22 may be formed by laminating a first photosensitive dry film on the substrate 20, and by patterning the stacked first photosensitive dry film. The chamber layer 22 may alternatively be formed by coating a liquid or wet resist on the substrate 20. Referring to FIG. 8, a second photosensitive dry film 26′ is stacked on the chamber layer 22 using lamination. Then, referring to FIGS. 9A and 9B, the second photosensitive dry film 26′ is patterned using photolithography to form a nozzle 27, thus forming a nozzle layer 26 on the chamber layer 22. FIGS. 9A and 9B are cross-sectional views of a completed inkjet printhead cut in directions perpendicular to each other.
The method illustrated in FIGS. 7 through 9B may be an improvement upon the method depicted in FIGS. 1 through 6B in so far as it utilizes photosensitive films to form the chamber layer 22 and the nozzle layer 26, and may thus allow better control of the thicknesses of the chamber layer 22 and the nozzle layer 26 and/or simpler overall manufacturing process. However, further improvements upon the above described conventional fabrications processes of thermal inkjet printhead may be desirable.